Thylacopteris minuta K.Hori & Khine, 2022

Hori, Kiyotaka, Khine, Phyo Kay, Fujiwara, Tao, Shin, Thant & Schneider, Harald, 2022, Thylacopteris minuta (Polypodiaceae), a new fern species from Myanmar, PhytoKeys 199, pp. 141-153 : 141

Thylacopteris minuta K.Hori & Khine sp. nov.

Diagnosis.

Thylacopteris minuta is similar to T. papillosa with 20-40 sclerenchyma strands per rhizome in cross-section. However, T. minuta is distinct from T. papillosa with sori shallowly sunken vs. T. papillosa sori deeply sunken. In addition, the lamina of T. minuta has a maximal length of 15 cm vs. a maximal length of 59 cm in T. papillosa . Thylacopteris minuta is distinct from the New Guinea endemic T. diaphana , which lacks sclerenchyma strands in the rhizome, has superficial sori, and lamina with a maximal length of 45 cm.

Type.

Myanmar: Shan State; Ah Lel Chaung reserve forest, Ywangan Township . 20°59'44.8"N, 96°34'26.81"E, ca. 1325 m, 30 Sep. 2019, K. Hori, P.K. Khine [ “Kine”], T. Fujiwara, M. Nagashima, P.P. Shwe & A.K. Moe 108601 (holotype: MBK 0328421 (herbarium barcode), Figs 2 - 5 isotype: HITBC, RAF) .

Epilithic.

Rhizome long-creeping, weakly branched, 1.0-2.0 mm in diam. (without scales), light brown, densely clothed with scales, phyllopodia sometimes prominent, these 1.0-2.0 mm high, 5.0-10.0 mm apart; 20-40 black sclerenchyma strands in rhizome, longitudinal, scattered in the ground tissue. Rhizome scales evenly inserted, dull brown, fragile, adpressed or apically spreading, quite densely set, deciduous, deltoid or ovate, 1.0-1.5 mm long, 0.5-1.0 mm wide, gradually narrowed from base to apex, sometimes with wavy margins, apex acute or rounded. Cell walls of rhizome scales dark brown, jigsaw-puzzle-shaped and wavy at basal and central part of scales, thickened, densely warty, in a single layer or double layers in basal scales. Fronds monomorphic, articulate to rhizome, petiolate. Stipes glabrous, 3.0-5.0 cm long, 0.7-1.0 mm diam, yellowish green. Blades membranous, lanceolate, 7.0-15.0 cm long, 2.0-4.0 cm wide, equally wide all along or rather wider above the basal part, pinnatisect, yellowish green. Segments glabrous, 20-30 pairs, lanceolate, ascending at an angle of 90°, 0.8-2.3 cm long, 0.3-0.5 cm wide, apically obtuse, entire at basal margin, crenate at apical margin, lower segments sometimes reduced, apical segments continuously reduced, terminal segments adnate or caudate. Veins free, once-forked, excurrent with terminal hydathodes. Sori exindusiate, uniserial on each side of costa, placed medially between costa and margin, shallowly sunken, 0.5-1.0 mm in diam., depth of papillae 0.2-0.5 mm, paraphyses absent. Sporangium globe-shaped, long stalked, 200-250 µm in diam., annulus vertical, indurated cells 10-13. Spores bilateral, oblong, light yellow, 40-60 µm long, 25-35 µm wide in lateral view, laesura 20-25 µm long, exospore smooth, perispore thin, surface shallowly wrinkled, globules absent.

Distribution.

Myanmar.

Habitat.

Epilithic, growing on shady surfaces of limestones (1-3 m high) in semi-evergreen or evergreen forest; altitude 940-1450 m.

Etymology.

The name refers to the relatively small size of this species compared to other species of Thylacopteris .

Additional specimens examined.

Myanmar: Shan State; Phaya Taung, Lein Le village, Paunglang Reserve Forest, Pinlaung Township ; 19°59'41.0"N, 96°39'3.0"E, ca. 947 m alt., 13 Sep. 2015, Y . Baba, K. Kertsawang, C. Kilgour, C. Puglisi, M. Rodda, P. Srisan-ga, T. Shin & P.P. Hnin 103191 (MBK0306471, duplicates on RAF, QBG). ibid., road between Nyaung Phyu village and Pinglaung village, Paunglang Reserve Forest, Pinlaung Township; 20°02'56.1"N, 96°46'00.1"E, ca. 1448 m alt., 16 Sep. 2015, ibid., 103361 (MBK0313746, duplicates in RAF, QBG) .

Notes.

The genus Thylacopteris is sometimes confused with Goniophlebium and Polypodium ( Rödl-Linder 1994; Fraser-Jenkins 2020). Warty cell walls of rhizome scales (Fig. 3 ) can be used to conclusively identify the genus Thylacopteris ( Rödl-Linder 1994).

Figures

Figure 2. Thylacopteris minuta K. Hori & P. K. Khine (holotype, Hori et al. 108601 = MBK 0328421, illustration by K. Hori) A habit B abaxial view of a middle segment C adaxial view of a middle segment D cross-section of rhizome E spore F rhizome scales G sporangium. Scale bars: 5 cm (A 1 - A 3); 1 cm (B-C); 0.5 mm (D); 10 µm (E); 20 µm (F); 200 µm (G).

Figure 3. Warty, thickened cell walls of rhizome scales (MBK 0328421; photo taken using DP 20 microscope camera, OLYMPUS, Japan). Scale bar: 2.5 µm.

Figure 5. Thylacopteris minuta in its natural habitat (MBK 0328421). Scale bar: 5 cm. (Photo by P. K. Khine).